The present invention relates to a turbine wheel for a turbine engine, the wheel comprising a disk carrying blades having roots engaged in grooves in the periphery of the disk.
Typically, each blade of a turbine wheel comprises an airfoil carried by a platform that is connected to a root by a tang. In general, the blades are formed with internal channels for passing a flow of cooling air (EP A2 1 653 047).
The grooves in the disk are regularly distributed around the axis of the disk, and between them they define teeth. In the assembled position, the platforms of the blades are spaced apart from one another a little in the circumferential direction, and they are spaced apart a little from the teeth of the disk in the radial direction.
The tangs of the blades are spaced apart from one another in the circumferential direction and they define between them spaces in which damper members are mounted in order to dissipate the vibrational energy to which the blades are subjected in operation, by rubbing against their platforms (EP A1 0 062 558).
Those damper members also provide radial sealing between the blade platforms by bearing radially against the radially inner faces of the platforms.
The blades are held axially in the grooves of the disks by means of annular plates that are mounted respectively on the upstream and downstream faces of the disk and that bear axially via their peripheries against the blade roots.
In operation, a leakage air flow referred to as the “bleed” flow passes radially from the inside towards the outside upstream from the upstream plate, and part of that flow is injected into the gas stream through the turbine. Another part of that flow passes axially between the outer periphery of the upstream plate and the blade platforms and flows from upstream to downstream over the teeth of the disk in order to ventilate them.
Proposals have already been made to use this portion of the bleed flow to cool the blade platforms, given that they are subjected to high temperatures in operation. One solution consists in making circuits for passing cooling air through the above-mentioned members that are formed by relatively thick blocks of material. The air that passes in those circuits is designed to strike against the inside faces of the platforms (see for example EP A2 2 110 515). Another solution consists in forming air flow spaces between the inside faces of the platforms and damper members in the form of sheet metal clips, those members being drilled to feed those spaces with air from the bleed flow (FR 11/53373).
Nevertheless, those solutions do not enable accurate control to be obtained over the flows of air for cooling the blade platforms. In the prior art, the air that is used for cooling the platforms comes from a bleed circuit in which the air flow rate is not calibrated, which means that it is not possible to define accurately the flow rates of air used for cooling the blade platforms.
Furthermore, in the prior art, it is not possible to cool certain zones of a blade with the air flowing in the internal channels in the blade. It is not possible to drill orifices in the platform that open out into the internal channels in the blade, since such orifices would be too complicated to make and would need to pass via zones of the blade that are highly stressed in operation and that must therefore not be weakened by drilling (in particular the zones where the platform is connected to the tang of the blade).
A particular object of the invention is to provide a solution to the problems of the prior art that is simple, effective, and inexpensive.